Polyurethane-insulated wires are widely used for wiring and coils in electronic equipment because of their inherent solderability without exfoliation of the insulating film.
Recently, while increased miniaturization and performance of electronic apparatuses has resulted, increased thermal resistance in electronic components has been demanded because of high temperatures at which the electronic apparatuses are used.
Conventional polyurethane-insulated wires cannot meet the recent requirements for thermal resistance in some applications. In such applications, attempts have been made to use polyester-insulated wires and ester-imide-insulated wires.
The polyester-insulated wires or the ester-imide-insulated wires, however, are not solderable, although these wires satisfy the requirement for thermal resistance. As a result, users of these wires are compelled to choose thermal resistance or the easiness of end treatment (solderability). Therefore, an insulated wire having both thermal resistance and solderability has been demanded.